Generally, cold production addresses a constantly changing need and, these days, represents a significant proportion of world electricity consumption used notably for conditioned air and the conservation of foodstuffs, and this despite the fact that the efficiency of the conventional refrigeration techniques based on gas compression and expansion remain inadequate.
The first refrigerants such as ammonia, sulfer dioxide, carbon dioxide or methyl chloride were very poisonous to people and the environment. They were replaced by chlorofluorocarbons, which were themselves prohibited in the early years of the new millenium because of their contribution to the greenhouse effect and the damage to the ozone layer. This problem remains since the hydrochlorofluorocarbons that are currently used continue, in lesser proportions, to have the same damaging effects as the earlier refrigerants.
In this context, there is therefore a two-fold advantage, energy-wise and environment-wise, in developing new cold production techniques that make it possible, on the one hand, to eliminate the refrigerant gases and, on the other hand, improve energy efficiency. Alternative techniques that can notably be cited include: thermoacoustic refrigeration, thermoelectric refrigeration or even magnetic refrigeration.
The latter relies on the magnetocaloric effect (EMC) of certain materials, which consists of a variation of their temperature when they are subjected to a magnetic field. It is thus sufficient to subject these materials to a succession of magnetization and demagnetization cycles and to perform a heat exchange with a heat-transfer fluid to obtain the widest possible temperature variation. The efficiency of such a magnetic refrigeration cycle exceeds that of a conventional refrigeration cycle by approximately 30%.
This energy saving that can be achieved with magnetic refrigeration makes it particularly interesting for domestic or industrial air conditioning or refrigeration applications.
The magnetocaloric effect (EMC) is at its maximum when the temperature of the material is close to its Curie temperature, the Curie temperature (Tc) being the temperature at which the material loses its spontaneous magnetization. Above this temperature, the material is in a disordered state called paramagnetic state.
Some magnetic materials such as gadolinium, arsenic or certain alloys of MnFe type exhibit magnetocaloric properties that are particularly well suited to the abovementioned applications.
Among these alloys, and notably based on Si, it is known practice, depending on the Curie temperatures sought, to be able to use alloys based on LaFeSiCo or based on LaFeSi(H). The insertion of light atoms such as hydrogen or cobalt into the LaFeSi compounds can be an effective way of increasing the Curie temperature while keeping the EMC effect of the material high. Such materials are particularly interesting because of their magnetocaloric properties combined with production costs, allowing for mass market applications, that are more favorable than those of materials such as gadolinium.
Generally, to exploit the properties of such magnetocaloric materials, the magnetic cold technology relies on the interaction of these materials with a heat transfer liquid that can be water-based.
The material heats up almost instantaneously when it is placed in a magnetic field and cools down by a similar thermal dynamic when it is removed from the magnetic field.
During these magnetic phases, the material is passed through by the liquid, called heat-transfer liquid, which will either be heated up on contact with the material during a so-called magnetization phase, or be cooled down on contact with the material during a so-called demagnetization phase.
Conventionally, the heat transfer fluid circulates in rectilinear channels or emergent pores that exist in the magnetocaloric material, this circulation corresponding to laminar mode hydraulic flow of the fluid, so as to obtain a maximum exchange surface area, with a minimum hydraulic head loss.
Thus, a cycle comprises:                a magnetization phase (magnetic state=1);        a demagnetization phase (magnetic state=0)which is reflected in energy available in each phase.        
This cycle is repeated up to frequencies of several hertz. When the frequency increases, the thermal power (for example: the cooling) delivered by the apparatus also increases.
For this power to increase in proportion to the increase in frequency, it is necessary to have heat exchange characteristics between the material and the liquid which make it possible to increase this thermal flow.
The geometry of a part made of magnetocaloric material is therefore essential to ensure an optimum heat exchange between said part and the heat transfer fluid which circulates in contact therewith.
It is known practice to use lamellar structures of magnetocaloric material that allow the circulation of fluid between said blades and thus increase the exchange surface areas with the heat transfer fluid.
It is then necessary to reproducibly, constantly and very accurately gauge the distances between said blades of material so as to best control the heat exchange processes. This necessitates the use of mutual blade positioning elements while ensuring the control of the geometrical parameters necessary for obtaining satisfactory heat exchange characteristics.